Hair tinting is a chemical process. In order to understand the techniques of tinting, it is important to know as much as possible about the chemistry and structure of the hair.
The growing part of the hair lies within a tubular indentation of the skin called the follicle. The bottom of the follicle is penetrated by a small upward-growing projection of connective tissue called the papilla,
Structure of the Hair
on which the hair bulb is formed. The part of the hair inside the follicle is the hair root. The part outside is the hair shaft. Popularly in tinting we speak of "root" as hair adjacent to scalp.
Each hair follicle is supplied with one to six sebaceous or fat-produc ing oil glands. Their function is to supply an oily wax of butter-like consistency to lubricate the hair and give it lustre and to protect it from dry atmosphere. Decreased secretion causes dry hair, while over-functioning causes seborrhea and oily hair and skin. Less wax is excreted in cold weather. Children have less oil in their hair than adults. The oily excretion increases sharply in puberty and the last months of pregnancy and on a diet especially rich in carbohydrates and fats. With progressing age, the secretion decreases, causing dry scalp and hair so common in later years. The decrease in the secretion occurs in women at about the age of 40 and is much slower in males.
GROWTH OF THE HAIR
The average age of a hair is two to five years. After it reaches the end of its life span, the old hair leaves the papilla, and a new column of cells is formed in or near the old follicle. Hair growth and formation are depend ent on hormonal glands, general nutrition, and local scalp conditions.
THE HAIR SHAFT
For the purpose of haircoloring, the part of the hair in which we are interested is the hair shaft, since this is the only portion to which color ing is applied.
Under the microscope the hair shaft reveals three different cell layers. The outermost is called the cuticle. The innermost part is called the medulla and may be present only intermittently, and is often com pletely absent from the hair. The part between the cuticle and medulla represents the bulk of the hair and is called the cortex. In addition mem brane-like structures are present in the cuticle and between cuticle and cortex.
Hair shaft is covered with a cuticle layer of horny, flat cells.
The cuticle of the hair shaft is composed of horny, flat cells which lie on the surface of the hair in overlapping formation, much like fish scales or the shingles on a roof. These cells contain no pigment, and are translucent. The tooth-like edges of the cuticle are projected upward and are affected by combing and brushing. When hair is combed or brushed away from the scalp these edges are left smooth; combing or brushing in the opposite direction causes damage. To allow tint to penetrate to the cortex, these scales must be opened up or "softened."
In tinting, in order to keep the haircolor natural looking, the coloring must penetrate inside the hair shaft. No coloring should be deposited on the cuticle layer. When the cuticle layer becomes colored, and this only happens when coating types of dyes are used, the hair no longer looks natural.
The cuticle and the membrane are sometimes resistant to penetration of the dye inside the hair shaft and it becomes difficult for tints to penetrate inside the hair shaft. If this happens, hair must be pre-softened, pre-bleached or other techniques used, to make the hair receptive to tints.
The cortex is composed of longitudinally arranged spindle-like hornified cells firmly adhering to each other. The natural pigment which gives hair its color is found in this layer. It is in the cortex layer that color changes are made during bleaching and tinting.
The medulla is often absent and is unimportant in haircoloring.
EYEBROWS & EYELASHES
The changes in color of the eyebrows and eyelashes are not related
to the changes in the color of the hair on the scalp. Haircoloring must not be used on eyelashes or eyebrows, because there is no satisfactory method of giving a patch test in this sensitive area.
WHAT CAUSES COLOR IN HAIR
The color of hair is determined in part by hereditary and racial
factors. Natural haircoloring is due to the presence of either brown or yellow and red pigments or a mixture of the two. It is important to understand these pigments because they affect the bleaching and tinting process.
Brown Pigment —The brown pigment is present in granular form. Little is known about its chemical nature except that it is combined with protein material. This makes it possible to change it with little difficulty.
For example, in bleaching, this pigment changes in a few minutes after the application of the bleach. The longer the bleach is left on, the lighter the hair becomes.
Yellow and Red Pigments —The yellow and red pigments contain iron and are present in granular and diffused form in the cortex cells. These diffused red pigments create the greatest problem in tint and bleach work.
The diffusion of the red pigment makes it difficult to destroy. This is especially apparent when preparing dark hair for silver or ash blonding. The reddish gold stage is reached in 20-30 minutes, while it frequently takes hours to bleach hair from this stage to a pale blonde.
These yellow and red pigments also cause dark shades to have reddish highlights, even when a drab tint is used.
WHAT CAUSES GRAY HAIR
The pigments are produced in the hair papilla and deposited in the
basal cells which are later converted into the spindle-like cortex cells and are moved upward with the growing hair shaft.
Gray hair is produced by a strong reduction of the pigment. The remaining pigment granula are irregularly distributed throughout the cortex.
New gray or white hair grows from follicles where dark hair has been shed, and in some cases dark hair grows out of follicles where formerly white or gray hair has been observed.
In ordinary graying, the process is gradual. Starting at the temples, the graying progresses slowly until complete gray or white hair develops.
Prolonged nutritional deficiencies affect the color of hair, but no proof has been obtained that feeding of specific vitamins will stop or retard graying under normal conditions.